Stephenville , Texas -LRB- CNN -RRB- Even with a conviction , the `` American Sniper '' murder trial never answered the one question that still haunts the families of Chris Kyle and Chad Littlefield .

Why were the two men killed while trying to help Eddie Ray Routh ?

There have been a series of confusing and incoherent explanations for Routh 's motives the afternoon of February 2 , 2013 .

We know Kyle sensed tension as he and Littlefield drove the former U.S. Marine to a gun range for an afternoon of bonding and helping Routh cope with what his family members believed was post-traumatic stress disorder .

Kyle secretly texted Littlefield , sitting next to him in a pickup , to say Routh was `` straight up nuts . '' Kyle 's wife , Taya , `` could tell something was up '' that afternoon when she spoke to her husband . Kyle sounded `` irritated , '' she has testified , then he never responded to a text asking if he was OK .

Yet Routh did n't reveal a clear reason in the fatal shootings . Kyle was shot four times in the back and once in the face . Littlefield was shot five times in the back .

Instead , the jury heard a series of bizarre explanations for why Routh allegedly turned the guns on Kyle and Littlefield .

Routh 's attorneys said the former Marine suffers from psychosis , paranoia and schizophrenia . Prosecutors argued that Routh is a `` troubled man '' who struggles with a `` personality disorder , '' not insanity .

` Legend ' looms over murder trial

The arguments were in direct contrast to one another . While Dr. Randall Price , a forensic psychologist who testified as the prosecution 's medical expert , said Routh 's heavy marijuana use caused a `` substance-induced psychotic disorder , '' Dr. Mitchell Dunn said his opinion was that Routh 's `` psychosis was not substance-induced . ''

`` It is my opinion that he was suffering from a severe mental disease or defect that caused him not to know his conduct was wrong , '' Dunn testified .

One piece of evidence -- video from the police car after Routh 's arrest -- shows the accused shooter complaining of mental problems and confusion .

`` I 've been so paranoid-schizophrenic all day , I do n't know what to even think of the world right now , '' he told the officer . `` I do n't know if I 'm insane . Or sane . I do n't know what 's even sane in the world right now . ''

Gene Cole worked as an officer in the Erath County Jail where Routh has been held since his arrest in the killings . Cole testified he heard Routh talk about the shootings four months after the tragedy .

`` I heard Mr. Routh say , ' I shot them because they would n't talk to me . I was just riding in the back seat of the truck and nobody would talk to me . They were just taking me to the range so I shot them . I feel bad about it , but they would n't talk to me . I 'm sure they 've forgiven me , ' '' Cole said .

Family : Routh acted bizarrely for years

In May 2013 , Routh did a phone interview from jail with New Yorker magazine writer Nicholas Schmidle . Portions of the recorded conversation were played for the jury .

Routh described being annoyed with Kyle and Littlefield as they made the 90-minute drive from his home to the countryside gun range .

Routh did n't trust the Navy SEAL and his friend after their first meeting , he told Schmidle .

`` That 's how I felt that day , '' Routh said on the recording . `` It was the smell in the air that morning . It smelled like s ** t. ''

Routh continued , `` It smelled like sweet cologne . I guess it was love and hate , you know . I was smelling love and hate . They were giving me some love and hate . ''

Later in the phone call , Routh complained that Kyle and Littlefield stopped to feed him at a fast-food restaurant on the way to the range . It was `` strange '' because he was n't hungry , and he felt the two men were trying to `` force feed '' him , Routh said to Schmidle .

Routh 's attorneys have suggested it was the arsenal of firearms lying next to Routh that triggered his psychosis and paranoia on the car ride .

`` At the time of this tragedy , Eddie Routh was insane , '' defense attorney Tim Moore said . `` Not only was he suffering from a severe mental disease or defect , not only did he not know his conduct was wrong , he thought he had to take their lives because he was in danger . ''

Routh said that when the men started shooting pistols at the gun range , he saw it as a showdown .

`` So we 're shooting pistols here , huh ? '' Routh recalls telling Kyle and Littlefield during his conversation with Schmidle . `` Again , that 's pretty much saying , ` Duel mother **** er . ' ''

When Schmidle asked what triggered him picking up a firearm and shooting Kyle and Littlefield , Routh replied that he was angry that Littlefield would not participate in the shooting .

`` I asked him a couple of times , ` Hey , are you gon na shoot ? ' '' Routh said . `` This is n't a spectator sport . It 's a shooting sport . You shoot . And that 's what got all , you know , wired up . ''

After that exchange , Routh said , `` I took care of business and then I got in the truck and left . ''

After deliberating less than three hours , a Texas jury found Routh guilty of capital murder in the case . Judge Jason Cashon immediately sentenced him to life in prison without parole .

CNN 's Jason Morris contributed to this report .

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The motive for Chris Kyle 's killing remains unclear

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Routh provided a series of bizarre statements to explain the shootings